Recently, a variety of types of optical discs have been proposed as a recording medium that can be removed from a recording apparatus. These recordable optical discs have been proposed as a large capacity medium of several GBs and are thought to be promising as a medium for recording AV (audio visual) signals, such as video signals. Among the digital AV signal sources (supply sources), to be recorded on this recordable optical disc, there are CS digital satellite broadcast and BS digital broadcast. Additionally, the ground wave television broadcast of the digital system has also been proposed for future use.
The digital video signals, supplied from these sources, are routinely image-compressed under the MPEG (Moving Picture Experts Group) 2 system. In a recording apparatus, a recording rate proper to the apparatus is set. If digital video signals of the digital broadcast are recorded in the conventional image storage mediums for domestic use, digital video signals are first decoded and subsequently bandwidth-limited for recording. In the case of the digital recording system, including, of course, the MPEG1 Video, MPEG2 video and DV system, digital video signals are first decoded and subsequently re-encoded in accordance with an encoding system for the recording rate proper to the apparatus for subsequent recording.
However, this recording system, in which the supplied bitstream is decoded once and subsequently bandwidth-limited and re-encoded prior to recording, suffers from deteriorated picture quality. If, in recording image-compressed digital signals, the transmission rate of input digital signals is less than the recording rate for the recording and/or reproducing apparatus, the method of directly recording the supplied bitstream without decoding or re-encoding suffers from deterioration in the picture quality only to the least extent. However, if the transmission rate of the input digital signals exceeds the recording rate of the recording and/or reproducing apparatus, it is indeed necessary to re-encode the bitstream and to record the re-encoded bitstream, so that, after decoding in the recording and/or reproducing apparatus, the transmission rate will be not higher than the upper limit of the disc recording rate.
If the bitstream is transmitted in a variable rate system in which the bit rate of the input digital signal is increased or decreased with time, the capacity of the recording medium can be exploited less wastefully with a disc recording apparatus adapted for transiently storing data in a buffer and for recording the data in a burst fashion than with a tape recording system having a fixed recording rate imposed by the fixed rpm of the rotary head.
Thus, it may be predicted that, in the near future when the digital broadcast is to become the mainstream, an increasing demand will be raised for a recording and/or reproducing apparatus in which broadcast signals are recorded as digital signals, without decoding or re-encoding, as in a DataStreamer, and in which a disc is used as a recording medium.
If a recording medium having plural data, such as data of a program comprised of image data and audio data, recorded thereon, is to be reproduced by the above-described apparatus, there is presented a problem that, while the processing of determining a readout position of the AV stream from the recording medium or that of decoding the stream needs to be performed promptly responsive to a command from the user for random accessing or stream decoding, increasing difficulties are met in prompt execution of such processing with increase in the volume of data recorded on a recording medium.